相关疑难解决方法(0)

@ModelAttributeSpring MVC 的目的和用途是什么？

我有

Class Shape {
      //Implementation
}
Class Round extends Shape{
      //Implementation
}

控制器我有

@Requestmapping(value="/view/form")
public ModelAndView getForm(){
ModelAndView mav=new ModelAndView();
mav.addObject("shape",new Round());
}


@RequestMapping(value="/submit", method = RequestMethod.POST)    
public ModelAndView submitForm(@ModelAttribute("shape") Shape shape){
         if(shape instanceof Round){ //**Not giving positive result**

         }
    }

在Jsp

<form:form action="/submit" commandName="shape" method="post">

//form tags

</form:form>

当我用Round对象提交表单时.在控制器端,ModelAttribute没有给出Round的实例.它只给出形状的例子.这该怎么做